Electric drive systems include a variable reluctance motor, a power converter directing the power flow to main windings of the motor and an adjustable direct voltage source energizing the motor.
The VR motor can be either a VR motor incorporating n phases, where N.gtoreq.2, and having for any rotor position at least one winding whereof the inductance increases with movement of the rotor in one direction and having for any rotor position at least one winding whereof the inductance decreases with movement of the rotor in the said direction, yielding the motor to be reversible; or a VR motor being only one direction rotatable incorporating n phases, where N.gtoreq.1, having for any rotor position at least one winding whereof the inductance increases with movement of the rotor in a given direction, and including a rotor whose each pair of poles is double off-center spiral, as disclosed in U.S. Pat. No. 3,679,953 from Jul. 25, 1972 for a two phase motor. The motor phases compose either one or more groups in such a way that each group includes for any rotor position at least one phase whereof the winding inductance substantially increases with movement of the rotor, and where each phase belongs to only one group.
A power converter energizes a phase at rotor positions wherein the winding inductance substantially increases with movement of the rotor. The phase is energized by applying a direct voltage to its main winding throughout the energizing interval. The energization interval of a phase starts at the rotor position, called switch-on point, where the winding inductance is at its substantial minimum and ends at the rotor position, called commutation point, where the winding inductance is either equal to or smaller than its maximum and where the winding inductance of the other phase of the same group is at its substantial minimum and where the said other phase is to be energized. Such operation of a power converter provides the successive energizing of the phases composing a group, one by one and only one at any instant of time, except near the commutation point where a certain overlapping occurs due to switching technique. A power converter supplies unidirectional current pulse to a main winding during energization interval. The supplied current pulse has rectilinear waveform whose main feature is the instantaneous change of the current at the beginning and at the end of the interval. Each instantaneous change of the main winding current is interrelated to the instantaneous change of the auxiliary winding current.
The basic feature of a current flowing through an auxiliary winding are two short pulses having directions opposing each other. The auxiliary winding current changes instantaneously to the certain level at the beginning of each pulse and thereafter it smoothly changes to zero.
The first pulse is interrelated to the rise of the main winding current at the beginning of the interval and it produces the magnetic flux opposing the flux being produced by the main winding current. The second pulse is interrelated to the instantaneous collapse of the main winding current and it maintains the decreasing flux previously established by the main winding current.
The above described waveshapes are the basic features of the drives and distinguish the drive systems being subject matter of this invention from the well known systems.